A subscriber identification module, such as a SIM card, is subscriber-specific, whereby the subscriber equipments are not bound to a certain subscriber. A subscriber identification module, for example a SIM card or a GSM card, is a functional card or a smart card that is placed in the mobile equipment and that contains information required for subscriber identification and for encryption of radio traffic. In the present application, a subscriber identification module, for example, a SIM card, refers to a functional card, which can be removed from the mobile equipment and with which a subscriber can use the card-controlled mobile equipment.
It is therefore not necessary for the user to own a mobile telephone, but it is sufficient to have a subscriber identification module, such as a SIM card (Subscriber Identity Module), that is allocated by the operator of the mobile telephone system and that is, in a way, a phone card with which the subscriber can make (and receive) calls from any mobile equipment in the system.
The subscriber identification module can be a smart card which has the same outer dimensions as most common credit cards. An alternative form of a SIM card in hand-held mobile phones is the plug-in-SIM, which is a coin-sized element containing the electronics of the card. The plug-in-SIM is placed in a telephone so that it is not easy for the user to change it. A telephone may also comprise both a stationary plug-in-SIM and a card reader. If the card reader contains a card, the telephone is identified according to the external card. Otherwise the telephone is identified according to the stationary plug-in-SIM. In the present patent application, a subscriber identification module, for example a SIM card, refers to both plug-in-SIM and a smart-card SIM, unless otherwise mentioned.
GSM recommendation 02.17 (Subscriber Identity Modules, ETSI) generally defines the operation of the SIM card. It defines the terms related to the SIM card, sets the requirements for the security of the SIM card and for the functions of the highest level, and determines the tasks of the network operator and the information to be stored in the SIM card. It also determines the minimum requirements for a SIM card of a user interface of a telephone, such as a mobile phone, as regards, for example, the input and change of the personal identification number (PIN) of the user.
Further, GSM recommendation 11.11 (SIM Application Protocol, ETSI) describes in more detail the matters disclosed in the above-described GSM recommendation 02.17 by determining, for example, the protocol between the SIM card and the mobile equipment (ME), the content and lengths of the data fields of the SIM card, and matters related to the electrical and mechanical connection. GSM specification 11.11 assumes designers are able to realize both the software and hardware implementation of a SIM interface.
It is known in connection with mobile telephone systems that the mobile subscriber has an identity by which the subscriber equipment can be identified and which indicates, for example, the manufacturer of the subscriber equipment. The mobile phone networks comprise a function wherein the subscriber equipment identity, in the GSM system, the international mobile equipment identity (IMEI) of the subscriber, is checked, by requesting the equipment identity from the subscriber. The equipment identity of the subscriber is checked, for example, to ensure that the subscriber equipment may be used in the network, i.e., that the particular equipment is not stolen or indicated as faulty, which means that its use will not cause interference or other problems in the network. The detailed structure of a subscriber equipment identity in connection with the GSM system is described in GSM standard 03.03, Numbering, Addressing and Identification, version 3.5.0, January 1991, ETSI. The subscriber equipment identity can be typically requested from the subscriber, for example, whenever the subscriber equipment has established a connection with the mobile telephone exchange. One manner of requesting for the subscriber equipment identity of the subscriber is described in the GSM standard 09.02, Mobile Application Part Specification version 3.8.0, January 1991, ETSI, item 5.9.1, Figure 5.9.1. The section also describes how the subscriber equipment identity is then transmitted to the equipment identity register (EIR) that checks whether the subscriber equipment has the right to use the services of the mobile telephone system, i.e., the register checks the access right of the subscriber equipment. The connection from the EIR to the mobile telephone exchange via an F interface is described in item 5.1 of the same standard, especially in Figure 5.1.1.
The EIR or some other part of the mobile telephone network comprises lists according to, for example, the GSM standard 02.16 (International MS Equipment Identities version 3.0.1, 1992, ETSI). The lists contain subscriber equipment identities or a series of subscriber equipment identities and have list identifiers. The standard uses colors as list identifiers that naturally signify, for example numerical identifiers. White or a white identifier is the list identifier of the list consisting of all numerical series containing equipment identities that have been allocated by the operators using the same mobile telephone system, i.e. in this case, the GSM system, to the subscriber equipment that can be used in the networks concerned. These numerical series are set forth by only indicating the first and last numbers of the series, i.e., not by listing the identities of individual subscriber equipments. A list marked black or a black list identifier contains the identities of all the subscriber equipment that must be denied access to the mobile network or to the mobile equipment, for example, because the subscriber equipment concerned is faulty and might cause interference in the mobile system itself or because the equipment has been stolen.
When use of a subscriber equipment is to be prevented in the mobile network or when, for example, a disabling signal is to be transmitted to a subscriber equipment, the access right of the subscriber equipment must be checked, for example, in the above-described manner. A typical situation requiring preventing use of a subscriber equipment or closing of the equipment occurs when the subscriber or terminal equipment has been stolen and its use is to be prevented. In such a case, a closing message must be transmitted to the unauthorized subscriber equipment or the equipment must be rendered inoperative in some other manner.
As described above, it is known in the GSM mobile system that the mobile network checks the access right of a subscriber equipment by randomly requesting the identity data of the subscriber equipment from the equipment and by examining from its own equipment identity register (EIR) whether the use of the subscriber equipment is permitted in the network. However, the equipment identity of a subscriber equipment is not necessarily requested for, nor is the aforementioned checking performed in connection with each registration. Therefore, there may be long periods during which the access right of the subscriber equipment is not checked. On the other hand, it is possible, in the GSM system, to request the identity of the subscriber equipment, and thus, check the access right of the equipment randomly, at random intervals.
If the checks are random, the checks load the radio path, the equipment on the path, and the data links between the exchange concerned and the equipment database, even though there is no reason to suspect that the equipment of the subscriber is on the black list of the EIR.
Random checks do not prevent the use of a stolen equipment, if there happens to be no checks. This problem can be amended by performing checks more often, but this in turn loads the connections and equipment even more.
Yet another alternative for checking the access right of a subscriber equipment is to perform the check by the subscriber equipment identity in the EIR in connection with each registration.
Such transmission of the equipment data and checking of the data in the EIR performed in connection with each registration load the equipment and the system considerably, since it is then necessary to transmit over the radio path the subscriber equipment identity that may be rather long, for example, according to a standard of the TETRA system: 60 bits. It is not preferable to transmit an identity of such a length frequently over the radio path, since the frequent transmission requires a considerable amount of transmission capacity.